feat(rag): Support RAG SDK (#1322)

dbgpt/rag/__init__.py

@@ -1 +1,11 @@
 """Module of RAG."""
+
+from dbgpt.core import Chunk, Document  # noqa: F401
+
+from .chunk_manager import ChunkParameters  # noqa: F401
+
+__ALL__ = [
+    "Chunk",
+    "Document",
+    "ChunkParameters",
+]